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GENERAL SPECIFICATION FOR THE CIVIL

ENGINEERING AND BUILDING DESIGN AND CONSTRUCTION OF SECONDARY

SUBSTATIONS

SUB-03-017 Issue No. 6

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© SP Power Systems Limited of 35

1. SCOPE

This Specification outlines Scottish Power Energy Networks (SPEN) technical requirements for the civil design and construction of existing and new ground mounted secondary substations. The Constructor is entirely responsible for all aspects of the civil design and construction process.

This is a generic technical specification written in a manner that it may be used without alteration for all such works therefore certain parts may not be applicable to all secondary substation construction types. It is not designed to cover every eventuality or site-specific situation; however, prior agreement must be obtained in writing from SPEN to any variation to the guidelines provided in this Specification. Development of proposals for site-specific variation that are acceptable to SPEN shall be the Constructor’s responsibility.

As far as is reasonably practicable, this Specification shall also apply to works at existing SPEN substation sites, however; this will be determined on a site-specific basis by agreement with SPEN, taking into account technical feasibility, cost and site-specific risk.

2. ISSUE RECORD

This is a Reference document. The current version is held on the EN Document Library.

It is your responsibility to ensure you work to the current version.

Issue Date Issue

Author Amendment Details

January 2015 4 C Woodman Functional requirements for alternative enclosures to ‘indoor’ equipment.

October 2015 5 A J Rowley Compliance with new SPEN Fire Policy, update to NGTS 3.10 and general technical update.

December 2016 6 G Rees Section 10.3 added to consider existing sites. Update to 10.5.2 Flood Risk. Section 13 Building Services requirements updated. General Minor amendments

3. ISSUE AUTHORITY

Author Owner Issue Authority

Gareth Rees Senior Civil Engineer

Fraser Ainslie Engineering Design Manager

Martin Hill Head of Engineering Design and Standards

4. REVIEW

This is a Reference document which has a 3 year retention period after which a reminder will be issued to review and extend retention or archive.

5. DISTRIBUTION

This document is not part of a Manual maintained by Document Control and does not have a maintained distribution list.



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6. CONTENTS

1. SCOPE .......................................................................................................................................... 1

2. ISSUE RECORD ........................................................................................................................... 1

3. ISSUE AUTHORITY ...................................................................................................................... 1

4. REVIEW ........................................................................................................................................ 1

5. DISTRIBUTION ............................................................................................................................. 1

6. CONTENTS ................................................................................................................................... 2

7. GLOSSARY .................................................................................................................................. 3

8. RELATED DOCUMENTS ............................................................................................................. 5

8.1 British Standards: ................................................................................................................. 5 8.2 International Standards: ........................................................................................................ 5 8.3 SPEN Documents: ................................................................................................................ 5 8.4 National Grid Documents: ..................................................................................................... 5 8.5 Industry Documents: ............................................................................................................. 5

9. INTRODUCTION ........................................................................................................................... 6

9.1 Feasibility .............................................................................................................................. 6

10. GENERAL REQUIREMENTS ....................................................................................................... 7

10.1 Consents ............................................................................................................................... 7 10.2 Pre-Engineering Studies ....................................................................................................... 7 10.3 Existing Substation Sites ...................................................................................................... 8 10.4 Scheme Development (Detailed Submission) ...................................................................... 8 10.5 Design ................................................................................................................................. 10 10.6 Setting Out .......................................................................................................................... 13 10.7 Construction ........................................................................................................................ 13 10.8 As-Built Information ............................................................................................................ 14 10.9 Quality Assurance ............................................................................................................... 14

11. STANDARDS .............................................................................................................................. 15

12. CIVIL TECHNICAL REQUIREMENTS ....................................................................................... 16

12.1 General ............................................................................................................................... 16 12.2 Concrete ............................................................................................................................. 18 12.3 Masonry .............................................................................................................................. 19 12.4 Prefabricated Building Enclosures ...................................................................................... 19 12.5 Traditional Building Enclosures .......................................................................................... 20

13. BUILDING SERVICES TECHNICAL REQUIREMENTS ............................................................ 31

13.1 Heating & Ventilation .......................................................................................................... 31 13.2 Electrical Services .............................................................................................................. 32

14. POST-COMMISSIONING (RETURN) SITE VISIT ...................................................................... 34

15. DRAWINGS ................................................................................................................................. 35



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7. GLOSSARY

Adopt: Transfer of title, ownership, operation and maintenance responsibilities as defined in the adoption agreement.

Approved: Equipment that is Approved in accordance with SPEN documents for use or installation on the Company network.

CDM Regulations: Construction (design and management) Regulations.

Civil: Reference to civil or similar shall mean civil, structural and building engineering and shall apply to the design, manufacture, installation and demolition of all related permanent works.

Company: Refers to SP Distribution Ltd, SP Transmission Ltd and SP Manweb plc.

Container: Approved prefabricated containerised housing for 11kV and/or 33kV Switchboard(s) together with associated Control and Ancillary equipment within a secure Prefabricated Enclosure.

Constructor: The party, including SPEN, IEC or other Third Party ‘Turnkey’ Design-Build Contractors and Third Party New Connection Developers and Contractors (ICPs), having ultimate responsibility for provision of the 33kV Primary substation, including design, construction and CDM.

The ‘Constructor’ should also be read as the Designer or Contractor depending on the type of Contract.

Deemed to Satisfy: Considered fit for the Company’s purpose and compliant in principle with this Specification by and without further reference to SPEN.

‘D’ Type or ‘G’ Type Substation

Combined ring main unit and metering unit equipment with protection panel typically associated with third party generation connections.

Energisation: The application of Voltage to an item(s) of Equipment from the system.

Equipment: Switchgear, transformers, cables, overhead lines, surge arresters, voltage transformers, current transformers, protection & control, telecommunications, unit substations.

GRP Glass Reinforced Plastic

High Voltage (HV): An alternating current (AC) voltage exceeding 1000 volts measured between the phase conductors.

Indoor Equipment: Equipment designed solely for installation within a building or other housing where the Equipment is protected against wind, rain, snow, abnormal dirt deposits, abnormal condensation and frost.

Low Voltage (LV): An AC voltage not exceeding 1000 volts measured between the phase conductors.

National Environment Agency

Environment Agency (EA) in England & Wales and Scottish Environment Protection Agency (SEPA) in Scotland

NGTS: National Grid plc Technical Specification



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Outage: De-energisation of an item(s) of Equipment on the Company’s electricity network system.

Outdoor Equipment: Equipment designed to be suitable for installation outwith a building or other housing where the Equipment is not protected against wind, rain, snow, abnormal dirt deposits, abnormal condensation and frost.

Secondary Substation An assembly of High Voltage Switchgear and Transformers up to 11kV together with associated control and ancillary equipment where the lower voltage is 400/230V, all within a secure enclosure

S.C.A.D.A.: System Control and Data Acquisition.

SP Distribution Ltd: The Distribution Licence Holder for the distribution service area formally known as ScottishPower.

SP Transmission Ltd: The Transmission Licence Holder for the transmission service area formally known as ScottishPower.

SP Manweb plc: The Distribution Licence Holder for the distribution service area formally known as Manweb.

Switching Station A secondary substation containing only High Voltage Switchgear.

SPEN Scottish Power Energy Networks, operator of network assets on behalf of the Company.

Third Party New Connection Contractors

Suitably Lloyds/National Electrical Registration Scheme Accredited Contractors undertaking contestable work in the competitive connections market.

Transformers Reference to transformers shall mean transformers and reactors.

Unit Substation A Unit substation comprises an 11kV/400V transformer fitted with a directly mounted ring main unit and an LV fuse cabinet. Other combinations of directly mounted attachments to the transformer may also be used (e.g. cable box in lieu of HV switchgear or LV fuse cabinet).



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8. RELATED DOCUMENTS

It is important that users of the documents listed below ensure that they are in possession of the latest issues of the documents.

8.1 British Standards:

BS EN 206-1 Concrete. Specification, performance, production and conformity.

BS 5266-1 Emergency lighting. Code of practice for the emergency escape lighting of premises

BS 60529 Degrees of protection provided by enclosures (IP code).

BS 8000 Workmanship on building sites, codes of practice.

BS 8500-1 Concrete. Complementary British Standard to BS EN 206-1

8.2 International Standards:

IEC 61936-1 Power installations exceeding 1 kV a.c. – Part 1 “Common rules”.

8.3 SPEN Documents:

CAB-15-003 Handling and Installation of Cables up to and including 33kV

CAB-06-001 Approved Equipment Register - Cables & Cable Accessories

SUB-01-012 Substation Fire Protection Policy

SUB-01-018 Substation Flood Resilience Policy

SUB-02-006 Secondary Substation Installation and Commissioning Specification.

SUB-03-012 Distribution Primary & Secondary substation LVAC supply Distribution Equipment

SUB-03-013 Specification for prefabricated substation housings for 12kV & 36kV switchboards.

SUB-03-018 Specification for Prefabricated Glass Reinforced Plastic Enclosures.

SUB-03-025 General Specification for the civil engineering and building design and construction of Primary substations.

SUB-03-026 General Specification for the civil engineering and building design and construction of 132kV grid substations.

SUB-03-034 General Specification for the civil engineering and building design and construction of 275kV and 400kV substations.

8.4 National Grid Documents:

GENERAL for “National Grid”/“NGC”/“the Client” read “the Company”, for “the Contract Administrator read “SPEN” and for “Contractor” read “Constructor”.

NGTS 3.10 Series

Generic Technical Specification for Civil, Structural and Building Engineering”.

8.5 Industry Documents:

National Structural Steelwork Specification for Building Construction (BCSA Publication).



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9. INTRODUCTION

This document outlines SPEN technical specification requirements for the civil design and construction of existing and new ground mounted secondary substations. The Constructor is entirely responsible for all aspects of the civil design and construction process.

This technical specification shall be used for all secondary substations types including:

Outdoor Equipment installed within a prefabricated GRP type enclosure.

Indoor or Outdoor Equipment installed within a purpose built, discrete brick enclosure.

Equipment installed within a customer owned building

Certain sections within this specification may not be applicable to all aspects of a particular Secondary substation project. Furthermore, the Specification is not designed to cover every eventuality or site-specific situation.

Project specific deviations from the design-build principles and construction details within this Specification will be considered by SPEN where the Constructor can demonstrate to SPEN’s satisfaction that they offer an equivalent or better technical and/or lower risk solution. All such deviations shall be fully discussed and agreed with SPEN within timescales that do not adversely affect project objectives.

9.1 Feasibility

Once the requirement for a Secondary Substation has been established and the type of substation agreed with SPEN, it is important that during the initial design stage SPEN requirements detailed within this and other referenced specifications are given due consideration.

In order to avoid possible abortive effort and subsequent delay; the Constructor shall confirm at the earliest opportunity how SPEN requirements are to be met. This should be undertaken by forwarding preliminary layout drawings for comment to SPEN that demonstrate in particular the proposed means of achieving:

Minimised Outages, Outage periods and impact on Company assets;

Plant access / egress, including access routes and the method by which plant will be installed / removed;

24-Hour access / egress for SPEN personnel (NB access via third parties is not acceptable);

Emergency egress;

Fire segregation;

Cable entries / routes;

Natural ventilation to Outdoor Equipment (in particular transformers);

Unless expressly agreed otherwise with SPEN, avoidance of flood risk.

The preferred and optimum location for a substation is freestanding with access at ground level from the public highway. Freestanding substation enclosures shall have a minimum 1m clear level access around the sides and rear (inspection, maintenance and ventilation), a minimum 2m clear level access to the front (door opening and plant access) and SPEN shall have bespoke rights of access, operation and maintenance over this (not applicable where this is in the public domain, e.g. at a frontage abutting public highway or footpath).

Enclosed basement type substations will not be acceptable.

Proposals for drainage and/or flood defence systems that otherwise satisfy the above functional requirements but have a floor level set less than 150mm above the general surrounding ground level must be expressly agreed with SPEN at the feasibility stage of the process.



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10. GENERAL REQUIREMENTS

10.1 Consents

Consents matters are outside the scope of this document but the Constructor shall ensure that all necessary notices and permissions are in place and that any associated applicable conditions are discharged prior to commencement of construction with respect to the following, where they apply:

Land Acquisition or Lease arrangements.

Planning Approval

Building Control or Building Warrant Approval.

Fire Authority Approval.

Drainage discharge, including where applicable Controlled Activities Regulations (CARs) and legal rights to discharge for SPEN where this is other than direct to an adopted public system.

Environmental requirements (such as newt licences and the like).

Party Wall Etc Act.

Any other statutory consents that may apply.

10.2 Pre-Engineering Studies

10.2.1 General

The Constructor shall carry out adequate appropriate desktop and site-based Pre-Engineering Studies to provide the information necessary to ensure:

The safe transfer of design loadings to ground.

Compliance with respect to contamination and ground water risk.

That drainage discharge options are identified.

That environmental risks are identified and independently verified including ecology, noise nuisance and flood related risks.

The Constructor shall carry out any other studies considered necessary or appropriate on a site-specific basis, in particular for substations located in complex situations including for example; brownfield sites, infilled sites, potentially contaminated sites, where piling or ground improvement may be required or where there has been previous deep or shallow mine working activity (coal, salt, metals, etc..

Where ecology studies indicate that they are present, all traces of invasive plant species such as Japanese Knotweed and Himalayan Balsam shall be entirely removed as necessary for the purpose of the works in a controlled manner and provision made to prevent them from re-establishing in those areas.

Pre-Engineering Study records and reports shall be available for audit inspection by SPEN, including confirmation that:

Worst case design load combinations would be safely transferred to suitable ground of adequate bearing capacity and that the extent of any potential future settlement would not adversely affect the operation of the substation, its infrastructure or its equipment (including cables/cable entries and other services).

The substation operation would not be adversely affected by flooding.



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10.3 Existing Substation Sites

Additional visual inspection, non-destructive testing and intrusive testing/analysis shall be carried out as necessary to inform theoretical assessment such that suitability can be confirmed where it is proposed to utilise existing foundation plinths or superstructure supports as part of the new works.

10.3.1 Existing Buildings

Where it is proposed to utilise an existing building to house new plant / switchgear then a condition assessment of the building against the requirements of this Specification, should be undertaken.

The assessment should consider the buildings structural design integrity and ability to withstand a Disruptive Failure event. Additionally the main design and technical requirements of this specification should be assessed, with cognisance taken of all design and technical requirements detailed in this document.

Upon completion of the assessment a whole life cost analysis should be undertaken to identify whether refurbishment or replacement of the existing building is the most appropriate solution. Consideration of deviations from this Specification, which offer an equivalent or better technical and/or lower risk solution will be reviewed on a project specific basis and should be agreed with the SPEN Civil Asset Manager.

10.3.2 Demolition of Buildings with Attached Substations

Where it is identified that demolition works are to be undertaken, that potentially impact on SPEN assets, discussions with SPEN should be undertaken at the earliest possible opportunity. This will allow SPEN to assess the network and advise of the future requirements for the existing substation.

The Constructor will be responsible for all inspection, assessment, temporary works and construction works required to ensure that the remaining substation is in accordance with the requirements detailed in this specification following the completion of any demolition works.

Upon the completion of the works SPEN shall be notified such that they can carry out an inspection, at the cost of the Constructor, to determine that the final condition of the substation is in accordance with this specification.

10.3.3 Substation Earthing

The Constructor shall carry out adequate and appropriate Earthing Studies, from which the earthing design shall be developed. The resulting Earthing Report shall be available for audit inspection by SPEN.

10.4 Scheme Development (Detailed Submission)

10.4.1 General

Subject to preliminary layout (feasibility) drawings being acceptable in principle to SPEN, it shall then be the Constructor’s responsibility to develop the scheme in detail in accordance with this Specification. Proposed General Arrangement and Construction drawings shall be submitted to include plans, elevations and sections of the buildings, structures and external works and shall clearly indicate the main dimensions, material and forms of construction proposed by the Constructor as follows:

Site location plan showing the whole of the site and access route, together with surrounding landscape and land use;

General arrangement drawing(s) for buildings and/or containers/housings that include details of floor layout(s) and indicate dimensional access, operation and maintenance clearances



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between and around equipment – dimensions shall not be less than the minimum requirements illustrated by Typical Layout Diagrams appended to Specification SUB-02-006;

Sections, a minimum of two (one in each plane) for each enclosure, to include all cable entries and outgoing services, clear headroom to plant and relevant finished ground and floor levels;

Elevations for the overall substation in total, including doors and any natural ventilation to equipment enclosures (buildings/containers/housings);

Building services etc., e.g. small power, lighting, heating, ventilation, etc;

Earthing;

Signage;

Other relevant information as applicable.

Where applicable and considered appropriate by SPEN, typical deemed to satisfy substation layout drawings may be issued for guidance, either generic associated with this Specification or on a project-specific basis. Such drawings would indicate minimum dimensional requirements and would be based on optimum layouts for equipment, ventilation, plant/personnel access/egress and cable entry.

The Constructor shall make proper provision in the programme for both the design and construction and shall allow a minimum of 28 days for SPEN to comment on each design and drawing submission, including any proposed site-specific variation to this specification or associated typical deemed to satisfy details. The Constructor shall ensure that cognisance is taken of all such SPEN comments, however, acceptance of the Constructor’s design submissions by SPEN shall not relieve the Constructor of any design responsibility or any generic functional obligation of this Specification, nor shall it imply any liability on the part of SPEN.

10.4.2 Equipment Enclosures (Buildings & Housings/Containers)

10.4.2.1 General (Indoor & Outdoor Equipment)

SPEN utilise proprietary prefabricated and traditional conventionally built enclosures that are deemed to relieve and/or contain an internal pressure rise due to a disruptive failure of the plant by means of pressure relief lifting roof or panel relief systems and/or structurally robust traditional construction.

SPEN will only install equipment into or formally adopt Approved Equipment installed by others within equipment enclosures that satisfy the requirements of this Specification. Selection of a particular type of housing may be subject to varying operational and supply requirements that take precedence over considerations of appearance, cost, local environment, etc.

General functional requirements include:

The requirements of SUB-02-006;

Suitable access for and cover to high and low voltage cables;

Security, in preventing intrusion as well as unauthorised entry;

Designed natural ventilation cooling to heat generating transformers;

Minimum 2-hour fire segregation where substations are attached to or integral within third party buildings;

Design to eliminate flood risk, unless expressly agreed otherwise with SPEN.



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10.4.2.2 Indoor Equipment

Functional requirements for enclosures to Indoor Equipment shall additionally and/or alternatively include:

Weather-tight enclosure construction to prevent moisture ingress;

Suitable internal enclosure environment, in particular with respect to;

o Natural ‘trickle’ only ventilation and the elimination of moisture ingress or condensation;

o Compliance with current Building Regulation thermal insulation requirements as detailed in Table 4;

Sealed cable entries to prevent belowground ingress of moisture, gas and vermin;

Preclusion of surface water run-off entry.

SPEN accept that in exceptional circumstances particular site-specific environmental situations may demand consideration of alternative enclosure types. In such situations, the same functionality requirements shall be factored into the enclosure design, together with any other relevant factors that are specific to the designed solution.

10.4.3 “Deemed to Satisfy” Submissions

Detail drawing submission would not be required by SPEN where the Constructor proposes freestanding construction precisely in accordance with deemed to satisfy drawings that have been issued by and confirmed by SPEN as suitable on a project-specific basis, e.g. typically as listed in this specification – provided the Constructor confirms this in writing to SPEN together with written confirmation that proposed substations are on level sites with minimum clearance around in accordance with this Specification, that ground conditions are suitable and that there are no adjacent embankments, retaining walls, services or the like within influence distance of the substation.

10.5 Design

10.5.1 General

Civil and building infrastructure in its entirety shall be designed to meet the functional requirements of the Works for a minimum of 40 years. Where SPEN will subsequently adopt the civil and building fabric then life to first maintenance shall not be less than 15 years and the design and construction detail shall be such that ongoing maintenance is minimised.

Substation design shall take cognizance of Pre-Engineering Studies.

Substation design shall be such that no sprinkler systems, gas, water, drainage or other third party service pipes, cables or heating and ventilation ducts are detailed within, through or under substations.

Typical Substation Layout Diagrams referenced in SUB-02-006 indicate minimum dimensional requirements. These standards are based on optimum layouts for plant, ventilation, plant/personnel access/egress and cable entry. Constructors should note that where proposals for non-standard electrical layouts are acceptable in principle to SPEN these could lead to a dimensionally larger substation being required. Substation layout details with respect to non-standard electrical layouts, irregular shaped rooms and internal room projections such as columns or beam downstands shall be subject to the prior written acceptance of SPEN.

The Constructor shall adopt a design methodology that shall identify all significant factors in the design and ensure that proper attention is given to each factor at every stage in the design process.



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Dead, imposed and dynamic loadings/actions for approved equipment are available from the manufacturers.

The detailed design submission must be in the English language and shall be prepared in terms of SI units in accordance with the recommendations of applicable BS/BSEN documents. All dimensions shall be in millimetres.

10.5.2 Flood Risk

Wherever practicable Secondary Substations shall be located outside of the flood risk zones as detailed in Table 1.

License

Region

Risk of Flooding

Pluvial Fluvial Tidal

SPD 1:200 1:200 1:200

SPM 1:100 1:100 1:200

Table 1 – Flood Risk Zones

As far as is reasonably practical the Constructor’s substation design shall eliminate or adequately mitigate against the risk of such a flood adversely impacting the operation of the substation (loss of supply or damage to equipment).

SPEN accept that it will not always be practicable to eliminate flood risk in Secondary Substation locations, in these instances the extent to which the design addresses this shall be agreed with SPEN on a cost-benefit analysis basis.

In the instances where it is accepted by SPEN that it is not appropriate to locate the substation outside flood risk zone, then on a project-specific basis and as far as is reasonably practical the substation concrete plinth should be raised to a level above the relevant flood level shown in Table 1.

The design shall allow for climate change for a 50 year design life and 300mm freeboard to allow for uncertainties in data and modelling. Where climate change guidance is not available then a minimum of 200mm shall be applied.

It is considered unlikely to apply but such schemes shall incorporate any requirement for compensatory storage as required by the Flood Risk Assessment (FRA) and accepted in principle by the National Environment Agency.

The Constructor shall obtain the prior written acceptance of SPEN to all proposed design measures to mitigate flood risk prior to construction.

10.5.3 Structural Design

The structural design of the civil and building fabric is entirely the Constructor’s responsibility and shall be prepared, checked and approved to professionally recognised design Quality Assurance procedures by appropriately qualified and experienced engineers, preferably Chartered Civil or Chartered Structural Engineers. Calculations shall be available for audit inspection by SPEN and, where applicable, calculation information shall be included within the CDM Health & Safety File handover to SPEN.

Low Voltage ‘LV’ distribution boards are wall mounted and therefore apply eccentric lateral dead load on supporting walls in addition to horizontal imposed loads arising during normal operational (link removal) or fault conditions (electrical trip).



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10.5.4 Disruptive Failure

Although substation equipment is extremely reliable and the probability of a disruptive failure due to internal arcing is very low this does have implications for both the design and location of substations, and the Constructor shall ensure that substation designers are aware that considerable internal overpressure and fireball may be produced when this condition occurs.

Rooms within buildings (etc.) enclosing High Voltage “HV” switchgear shall be designed such that they maintain their integrity and relieve or withstand the overpressure that can be developed during a disruptive failure under the most onerous simultaneous operation condition. Whilst it is not possible to measure or reasonably quantify the magnitude of any potential overpressure, experience over many years has demonstrated that the approved prefabricated Container housings and the typical robust traditional (masonry/reinforced concrete) construction enclosure details indicated by this Specification are generally adequate to relieve and/or reasonably contain this overpressure and are therefore the preferred and most appropriate forms of construction.

Designers shall give due consideration to the potential for such disruptive failure in locating egress routes and in structural civil design, in particular wall panels. Designers shall note that masonry panels to traditional construction enclosures housing High Voltage switchgear or transformers may require secondary steelwork support (e.g. wind posts) or other lateral structural reinforcement and that structural concrete slab roof construction may be necessary to provide lateral restraint to the tops of wall panels, even where this may be as a sub-roof beneath a superimposed pitched roof over.

In line with the CDM design obligation to limit the risk associated with disruptive failure the preferred and optimum location for a substation is freestanding and detached from other development and every effort shall be made by the Constructor to comply with this requirement. In the limited instances where there is a compelling reason that this is not practicable and location of a non-standard substation that is integral with other buildings is therefore essential and acceptable in principle to SPEN, designers shall ensure that the nature of the construction is such that progressive collapse and/or fire spread does not ensue in the event of a disruptive equipment failure.

10.5.5 Fire Risk

The Constructor shall be responsible for ensuring that any necessary approvals are obtained from applicable fire authorities. Where applicable, any necessary fire certification shall be included within the CDM Health & Safety File handover to SPEN.

In addition a site-specific risk assessment shall be carried out that shall consider:

The likelihood of members of the public being in the vicinity/close proximity;

The substation type and location with respect to property types and public areas;

The transformer, plant, and insulant type;

The access/egress arrangements for members of staff/contractors.

The Constructor shall assess the fire risk and shall provide no less than the minimum mitigation measures to enclosures for Indoor High Voltage Equipment and to oil containing Outdoor Equipment (e.g. transformers) in accordance with this Specification and SPEN substation Fire Policy SUB-01-012.

10.5.6 Drainage Discharge

Where discharge is not fully contained within land over which the Company’s has rights or is other than direct to an adopted public system, the Constructor shall confirm formal discharge consent approvals to SPEN and these shall be included where the CDM Health & Safety File is handed over to SPEN (i.e. legal rights to discharge for SPEN).



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10.5.7 Site Layout

Constructors shall note that pedestrian safety barriers may be required where the site layout is such that emergency egress from the substation is towards a vehicular traffic route, and that these barriers would be required to be demountable if this were also a plant access route for the substation.

Constructors shall note that vehicular crash barrier protection may be required external to the substation where the site layout is such that SPEN perceive there to be a risk of impact to the substation from vehicular traffic (e.g. substations adjacent to vehicle turning areas or where access roads are at a higher level).

10.6 Setting Out

It is essential that substations be set out in accordance with Land Acquisition drawings where the Company have or will subsequently take freehold or leasehold possession of the land on completion.

10.7 Construction

It is incumbent upon the Constructor to comply with all relevant legislation, including future updates and publications in keeping with industry good practice.

Typical Drawings listed in this Specification that may be available from SPEN that indicate typical deemed to satisfy construction details for various Secondary Substation types. Constructors shall note that unless otherwise expressly instructed by SPEN where issued these guide details are generic only with respect to such aspects as dimensions, handing, cable entries, etc..

The preferred construction details are SPEN’s “deemed to satisfy” construction details.

Some basic civil engineering and building technical compliance information is given in this Specification, over and above functional design and construction requirements, in order to assist in the initial development and costing of the civil aspects of substation projects.

The Constructor shall ensure that civil engineering and building contractors engaged to carry out works under this Specification are competent, qualified and experienced with respect to the nature of electricity substation construction. Civil and building contractors should hold appropriate membership of the National Federation of Builders, Federation of Master Builders, Civil Engineering Contractors Association or similar professional trade body. Operatives should hold appropriate Construction Skills Certification Scheme (CSCS) Cards or National Vocational Qualifications (NVQs); in particular welders shall be tested to meet and satisfy the requirements of the National Structural Steelwork Specification for Building Construction.

The standard of workmanship shall be in keeping with industry best practices and not less than that specified by BS 8000.

The Constructor shall ensure that civil engineering and building contractors engaged to carry out works under this Specification take all reasonable precautions to ensure the safety of all parties concerned with or affected by operations associated with substation construction works.

The safety or operation of any existing Company utility plant must not be prejudiced; records of buried services must be obtained from all utilities and safe-digging practices must be adopted, including the use of a cable-locating tool.

The Constructor shall notify SPEN prior to commencement of substation construction works.

Substation construction shall be such that no sprinkler systems, gas, water, drainage or other third party service pipes, cables or heating and ventilation ducts or are built within, through or under substations.



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SPEN will not install equipment into purpose built substation enclosures until and unless all building works, except post-commissioning finishing works, are complete and are in accordance with this Specification. Unless variation has been agreed in writing by SPEN prior to construction, a delay in plant installation or energisation could result if works are not in accordance with this Specification.

SPEN will not consider formal adoption of Approved Equipment installed and commissioned by others until and unless all building works to associated purpose built enclosures are complete and in accordance with this Specification, including receipt of As-Built information where applicable (i.e. in relation to adoption of enclosures such as buildings/containers).

10.8 As-Built Information

Operating Manuals and CDM Health & Safety Files shall be submitted to SPEN in an approved electronic format.

10.9 Quality Assurance

All materials shall be of good quality, suitable for purpose, designed and manufactured such that they provide safe and continuous service and are capable of withstanding the various stresses and onerous conditions to which they may be subjected to on the site of installation without suffering any undue deterioration.

The Constructor is responsible for and shall ensure that all the listed duties of The Contract Administrator are carried out and completed with respect to civil quality assurance in accordance with NGTS 3.10, in particular approval and sign-off of Inspections, Hold & Notification Points, Testing, Manufacturing Processes, Specialist Operative requirements and Document Submission - including off-site visits. This Clause shall not grant any right to the Constructor to vary the requirements of either this Specification or NGTS Specifications, nor shall it detract in any way from SPEN’s rights.

SPEN shall have the right to inspect any aspect of the construction process. The Constructor shall ensure that all civil design and testing output are available for audit inspection by SPEN.



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11. STANDARDS

Civil and building infrastructure in its entirety shall be designed and constructed to comply with the following documents, unless expressly varied by this Specification

SPEN Policy documents;

SPEN Specification documents;

NGTS 3.10. series document suite;

European Standards;

British Standards;

Codes of Practice;

Relevant Industry Guidance.

Some basic civil engineering and building technical compliance information that is contained within such documents is repeated within this Specification, over and above functional design and construction requirements, in order to assist in the initial development and costing of the civil aspects of substation projects.

Where associated Standards do not explicitly relate to civil, structural or building engineering but nonetheless contain requirements that may impact upon these aspects it shall be the Constructor’s responsibility to ensure a holistic and compliant overall design solution (e.g. in relation to earthing).

National Building Regulations requirements shall apply unless stated or expressly implied otherwise within this Specification. Where literal compliance is not possible the work shall be to a standard agreed with SPEN that takes the Building Regulations as its basis.



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12. CIVIL TECHNICAL REQUIREMENTS

12.1 General

12.1.1 Access

Constructors shall note that reliance on recourse to third parties for compliance with the SUB-02-006 requirement for unrestricted 24-hour access for SPEN operatives would not be acceptable; this must be controlled by standard Company suited locks.

Where vehicular crossings are required to highway footways or verges the design and construction shall be to the Local Authority’s approval and the Constructor shall be responsible for all notifications together with any associated fees.

Enclosures shall incorporate approach and perimeter edged-paving surfacing to and between doors (and to gates to compounds) to facilitate personnel access.

12.1.2 Earthworks

All foundations shall be set on undisturbed inorganic strata that provide the required minimum design safe ground bearing capacity.

The bottom of excavated areas shall be trimmed, levelled or graded and well rammed or otherwise compacted. The construction sequence shall be such that undue exposure of the formation level to excavations is avoided. Excavations shall be kept free from all water from whatever source.

Excavations to reinforced concrete foundations shall incorporate a minimum 50mm thick layer of blinding concrete.

12.1.3 Stone Chipping Compound Surfacing

Stone chipping surfacing shall not be less than 225mm overall depth of construction comprising an approved build-up of:

A 75mm thick layer of newly quarried clean angular stone chipping topping. 14-20mm distribution;

On a minimum 150mm thick layer of clean graded Type 1 granular sub-base, compacted in a minimum of two layers.

12.1.4 Drainage

Drainage systems shall meet the requirements of and be approved by relevant local authorities, utility companies and environment agencies as applicable.

The Constructor shall ensure that drainage schemes are adequately sized to accommodate flow rates that properly reflect the sources serviced by the system with pipes running un-surcharged at self-cleaning non-scouring velocities.

Surface water drainage systems shall be designed for storm conditions to an appropriate return-period for the substation.

12.1.5 Footways

Prefabricated paving systems shall comprise maximum 600x600mmx50mm thick precast concrete paving slabs on a combined minimum 125mm overall thickness of sand-cement bed on compacted imported Type 1 clean graded stone sub-base. Perimeters to paved areas that are not otherwise



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contained by buildings, structures or road kerbs shall be edged with a 200x50mm precast concrete edging set in a concrete haunch and foundation.

Cast in-situ concrete, asphalt or other alternative paving systems shall be subject to prior acceptance by SPEN.

12.1.6 External Site Finishes

Proposals for external site finishes shall be submitted to SPEN for comment.

Concrete surfaces shall be avoided over cable entry areas unless appropriate adequate proposals for ducting beneath or cable trenching through have been formally accepted in writing by SPEN.

12.1.7 Metalwork

All steelwork, including members internal to substation buildings, shall be hot dip galvanised and shall facilitate fixings for earthing tape.

A minimum thickness of 85 microns is required. This should be increased where necessary to take account of any site-specific factors that may accelerate the corrosion rate.

As required by the National Structural Steelwork Specification for Building Construction, nuts to galvanised bolt systems shall be of a higher grade than the bolts.

12.1.8 Metering Rooms/Cabinets

The preferred location for metering is within an integral or attached fully compartmented segregated enclosure that is accessed via a third party door.

Where alternative built-in ‘hole in the wall’ metering cabinets are acceptable to SPEN in lieu of segregated meter rooms these enclosures shall be secure and weathered to offer a degree of protection not less than that of IP44 to BS EN 60529. Furthermore, the construction of these cabinets shall be such that long object probes of any type and cross-section do not have the potential to infringe safety clearance distances from hazardous parts.

In addition these shall be:

Robust vandal and corrosion resistant construction with metal sub-frames and housings. Metal sub-frames shall be built-into masonry.

Bonded to the substation earth system.

Door construction to metering rooms/cabinets shall meet the requirements of this Specification and fitted with cylinder type night latch locks that will accept exchange Company suited barrels on completion. Doors shall be fully weathered including appropriate seals to the external perimeter of frames.



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12.2 Concrete

Unless expressly confirmed otherwise by the Constructor’s civil design, concrete shall be designed mixes of strength class not less than those indicated in Table 2.

Concrete Use

Strength Class (Grade) to:

BS EN 206-1 BS 8500-1

Max. Agg’ Size (mm)

Type of Concrete Finish

Type Description

Blinding Layer C16/20 20

Buried Unformed Surface: Buried worked surfaces produced without formwork.

Basic Finish: Concrete shall be levelled & screeded initially for a uniform plain or ridged surface as required for subsequent work

Mass Infill C16/20 40

Substructure (Below Ground Level): Formed finishes e.g. buried sections of buildings, bunds, equipment foundations.

C32/40 20

Buried Formed Surface: Buried surfaces produced with closely-jointed formwork.

Rough Finish: Forms designed to produce a dense smooth finish free from voids or honeycombing greater than 10mm and other large blemishes.

Substructure (Above Ground Level): Worked finishes e.g. to exposed top surface of equipment plinths, floor slabs (finished with anti-slip paint).

C32/40 20

Unformed Surface: Exposed worked surfaces produced without formwork.

Steel Trowel/Power Float Finish: Wood float finish as below to be steel trowelled under firm pressure or preferably power floated to produce a dense uniform smooth polished surface free from trowel marks or other blemishes.

Substructure (Above Ground Level): Exposed formed finishes e.g. to equipment plinth upstands.

C32/40 20

Formed Surface: Exposed surfaces produced with close-tolerance formwork.

Fair Worked Finish: Forms designed to produce a hard smooth surface with true, clean arrises. All surface blemishes and irregularities made good as specified (e.g. cement paste to green concrete). Concrete rubbed down after curing to produce a smooth and even surface.

Superstructure: Exposed worked finishes to in-situ or screeded roof slabs to receive waterproofing systems.

C32/40 20

Unformed Surface: Exposed worked surfaces that will subsequently be covered produced without formwork.

Wood Float Finish: Basic finish as above to be wood floated under light pressure initially to eliminate surface irregularities then under firm pressure after moisture film has disappeared and the concrete cured sufficiently to prevent laitance being worked to the surface.

Table 2 – Designed Mixes of Concrete

Exposure class and minimum cover to reinforcement shall be appropriate for the site and ground specific conditions in accordance with the civil design. Specified characteristic strength shall be verified by independent concrete cube tests.

A flat, level and smooth surface finish to floors and plinths is essential for the installation of plant to be acceptable to SPEN. The deviation from the underside of a 2m straight edge resting in contact with floors and plinths shall not be more than 3mm.

Exposed arrises to plinths shall be chamfered. Arrises to ramp transitions onto floors, vertical corners within cable trenches and the like over or around which cables could pass shall be rounded.



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12.3 Masonry

12.3.1 Masonry Units

Masonry materials shall be selected to maximise durability consistent with the architectural or Planning requirements for the substation.

The minimum acceptable standard for below ground masonry shall be High Density (HD) Category I clay brickwork of minimum 75N/mm² mean compressive strength, 7.0% maximum moisture absorption and durability designation F2 S2 (ex-‘Engineering Class B’ quality designation or equivalent).

External masonry shall be HD clay-facing brickwork of minimum 30N/mm² mean compressive strength, maximum 12% moisture absorption and durability designation F1 S1 or better. SPEN acknowledge that there may be certain site-specific situations where it is essential to propose the use of lower quality external masonry to meet Planning Authority or other aesthetic requirements. In such circumstances it may be necessary to apply an appropriate coating system such as a siloxane hydrophobic impregnation to ensure that undue moisture penetration is prevented.

Internal masonry enclosing rooms that house High Voltage Equipment shall be light coloured solid smooth fair-faced clay or concrete facing brickwork of minimum 20N/mm² compressive strength and maximum 12% moisture absorption.

12.3.2 Ancillary Items

Mortar grade shall be appropriate for the masonry type, including the use of sulphate resisting cement where necessary (e.g. in certain belowground conditions). In particular, mortar to internal concrete brickwork shall be Class iii.

Brickwork ties to cavity walls shall be stainless steel Type 1 or Type 2 construction evenly spaced and staggered in alternate courses. Where enclosing rooms that house High Voltage Equipment spacing shall be at maximum 450mm centres vertically and 450mm centres horizontally.

Where utilised, masonry bed-joint reinforcement shall be stainless steel construction.

Where utilised, built-in wind posts shall be galvanised or stainless steel construction.

Damp proof courses shall be incorporated and shall be either High Density (HD) Category I clay brickwork of minimum 125N/mm² mean compressive strength, 4.5% maximum moisture absorption and durability designation F2 S2 (ex-‘Engineering Class A’ quality designation or equivalent) or proprietary high performance (high load/strength, high bond) pitch-polymer systems.

12.4 Prefabricated Building Enclosures

12.4.1 Outdoor Type Equipment

Prefabricated GRP enclosures to Unit Substations shall meet the requirements of SUB-02-006 as specified by SUB-03-018.

Finished plinth level shall not be less than 75mm or more than 225mm above adjacent finished ground level.

12.4.2 Indoor Type Equipment

Prefabricated enclosures shall not be acceptable to substations that incorporate wall mounted Low Voltage ‘LV’ distribution Boards.



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Prefabricated enclosures that meet the requirements of SUB-02-006 as specified by SUB-03-013 shall be acceptable to HV only Switching Stations, provided insulation levels to walls and roofs comply with the thermal insulation values set out in Table 4.

Alternatively, for other types of Indoor Equipment such as ‘D’/’G’ Type Substations where the civil fabric of the substation will remain the responsibility of a third party Constructor or end-user and will not be adopted by the Company (SPM/SPD/SPT), SPEN will consider alternative, less costly, enclosure designs (including GRP) - subject to their performance being warranted by the proposer to provide an environment that is suitable for the safe and long term operation of Indoor type equipment. SPEN require a performance warranty before it will adopt and/or install its equipment in such enclosures, which shall satisfy the functional requirements listed below:

Provide a robust enclosure with a high level of security against unauthorised entry, including door furniture and locking mechanisms – Indoor Equipment presents a very significantly greater risk of injury or fatality in the event of unauthorised entry than Outdoor Equipment.

Provide a dry (~50-80% RH), temperature stable environment (5-20C for 95+% of time with a max of 30C), similar that which would exist in a brick enclosure. Typically this will require thermal insulation, control of solar gain and heating for the winter – note: active systems such as air conditioning will not be acceptable.

Provide insulation levels to walls and roofs that meet the thermal insulation values set out in Table 4.

Incorporate a sealed floor/substructure (sealed cable ducts etc.).

Provide adequate natural ventilation.

Provide sufficient access around the equipment to facilitate installation, maintenance, repair or replacement - or be such that it can be lifted off easily without compromising subsequent environmental control. Guidance on minimum dimensions can be found in the Typical Layout Diagrams appended to Specification SUB-02-006.

Include facilities for wall mounting of heavy equipment (units weighing approx 100-150kg).

Withstand an internal design guide overpressure as described in this Specification (wall panel design) OR facilitate the controlled release of pressure (e.g. pressure release panels, tethered lifting roof system etc.).

12.4.3 Performance Warranty

SPEN will only accept proposed dimensions and security arrangements for alternatively constructed enclosures. SPEN will NOT assess the likely performance of enclosures in terms of the functional requirements stated above. Constructors or their customers/end-users who receive a ‘point of connection’ from the Company’s distribution network at the customer substation will remain responsible, for the life of the connection, for providing an environment for the Company’s equipment that meets the functional requirements detailed in this document.

Parties supplied from or connected to substations utilising such enclosures should be aware that a clause will be included in their connection agreement indicating that a condition of their connection remaining energised is that the internal enclosure environment remains compliant with the functional requirements stated above.

12.5 Traditional Building Enclosures

12.5.1 General

Substation buildings shall be fully weatherproof, paying particular attention to design and construction details with respect to wind driven rain and storm water run-off.



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Substation buildings shall be designed and detailed such that the potential for vandalism and theft is minimised.

Where exposed metalwork within is acceptable in principle to SPEN this shall be bonded to the substation earth system with adequately sized insulated conductor.

Basement construction shall not be acceptable.

Substation enclosures shall not have windows.

12.5.2 Substation Layout

A clear passage of not less than 750mm wide shall be provided behind and around high voltage switchgear boards to HV (only) Switching Stations. This passage shall be clear of all obstruction including wall-mounted equipment.

12.5.3 Fire

Buildings shall be designed to prevent the propagation of fire generally and in particular in the event of an electrical failure from internal high voltage switchgear or power cable faults.

Although substation plant is extremely reliable and the probability of a disruptive failure is very low a fireball may be produced when this condition occurs and considerable heat and smoke can be generated as a result.

The maximum travel distance to a place of reasonable safety shall be in accordance with Table 3:

Room Type Containing

Building Regulations Purpose Group

Travel Distance - One Direction Only (m)

Travel Distance - One or More Direction (m)

Oil filled plant/ generator/battery room

Purpose Group 7 – Place of special fire hazard

9 18

Other rooms Purpose Group 6 – Industrial, normal risk

25 45

Table 3 – Maximum Travel Distances

A reasonable place of safety shall be:

A protected stairway enclosure (a storey exit);

A separate fire compartment from which there is a final exit to a place of total safety; or

The nearest available final exit.

Notwithstanding the table above, rooms enclosing switchboards in excess of 6m in length shall have a minimum of two exit doors, opening outwards, on or at opposite ends of the switch room, to allow egress in either direction from behind switchboards.

In addition, a minimum of two exit doors shall similarly be provided where SPEN deem this necessary for the safety of its operatives, e.g. as indicated in its typical “deemed to satisfy” substation layout drawings listed in this Specification.

Escape route passages shall have a minimum clearance width of 900mm and the clear opening width and height of doors forming part of this escape route shall not be less than 750mm and 2000mm respectively. Emergency exit doors shall open outwards, external doors by means of panic bars



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without the use of a key, which shall be clearly marked with a suitable notice explaining the operation of the opening device.

Signage indicating escape routes and self-contained emergency lighting shall be agreed with SPEN on a project-specific basis.

The use of readily combustible materials within substation buildings is not acceptable; all internal lining and structural surfaces shall be material of limited combustibility such that they adequately resist the spread of flame over their surfaces. In addition but with the exception of external doors, civil fabric finishes internal to the substation enclosure should meet the requirements of National Building Regulations Class O with respect to surface spread of flame.

Where it is required, fire protection to steel frame construction shall be by means of a reinforced concrete surround or proprietary intumescent paint or spray system, not fireboard that could be displaced in the event of a disruptive failure.

Substation buildings shall be fully compartmented construction with minimum 1-hour fire segregation, including below floor trenches and ducts passing between rooms, such that spread of fire to other internal areas shall not occur for a minimum period of 60 minutes in the event of a fire initiating.

Risk assessment with respect to fire and smoke spread to property surrounding substations is entirely the Constructor’s responsibility.

Portable fire extinguishers shall not be provided.

In the limited instances where there is a compelling reason that a freestanding substation is not practicable and location of a non-standard substation that is attached to or integral within other buildings is essential and acceptable in principle to SPEN compartmented construction shall be increased to a minimum 2-hour fire segregation. In addition it is accepted that the Constructor’s risk assessment could demand measures over and above those required by SPEN, in which circumstances it is important that such risk is addressed, in particular for integral substations that are within the boundaries of third-party properties offering personnel access or housing valuable contents. In such circumstances design and construction detail that adequately mitigates fire risk within these substations would be acceptable in principle to SPEN subject to the following minimum requirements:

Minimum 2-hour fire segregation.

Any appropriately greater period of fire resistance necessary to substation roofs having personnel access over shall be achieved by means of the design/construction of the concrete roof slab and not by fire boarding or the like that could be displaced in a disruptive failure;

The sheaths of traditionally used types of cable are either highly combustible or produce noxious gases and smoke once ignited, which increases respectively the probability of fire starting/propagating along cable routes and the potential impact to human life and property once fire is established. Low smoke and zero halogen (LSOH) sheathed cables shall be used therefore to significantly reduce this risk. Such cable routes shall have robust 1-hour fire segregation that is capable of withstanding accidental mechanical damage;

The presence of insulating oil within transformers increases the risk posed from fire and smoke therefore an approved alternative dielectric insulating fluid such as Synthetic Ester Insulant (e.g. Midel) shall be used to significantly reduce this risk. The Constructor shall note that Midel is more difficult to ignite than mineral oil, produces only approximately 30% smoke density and all combustion products are non-toxic;

Incorporation of third-party owned and maintained fire and/or smoke detectors.



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12.5.4 Oil Containment

The Constructor shall be responsible for compliance with any local authority and/or national Building Control requirements with respect to oil containment generally within substations that are attached to or integral within other buildings.

12.5.5 Security

Substation security is of prime importance and buildings generally shall be designed and detailed to minimise the potential for vandalism and unauthorised entry. Any additional security measures over and above the requirements of this Specification shall be determined by Scottish Power Corporate Security who shall be consulted on a project-specific basis.

Where substation locations are identified as being at risk from vandalism or unauthorised entry the security requirements shall take precedence over considerations of appearance, cost and local environment. In these circumstances any boundary fencing shall be security standard, doors shall be proprietary metal security doors and additional security measures over and above those indicated by typical or deemed to satisfy details may be necessary by express agreement with SPEN.

12.5.6 Earthing to Metal Door Sets

The Constructor shall be responsible for provision earthing connections to metal door sets as follows:

Appropriately sized (minimum 70mm²) flexible anti-fatigue braided copper connections top and bottom between frames and leaves;

Appropriately sized (minimum M10) stud projections to each side of frames at a height of approximately 1.2m above finished floor level.

12.5.7 Floors

Wherever practicable, floors should be full bearing monolithic in situ concrete slabs. The required finish and permitted tolerances for floor finish given in this Specification are important for plant installation and operation.

Structural floor slabs shall be continuous at doorways. Sand fill with screed topping or suspended cover systems will not be acceptable to trenches at these locations.

Screed finishes to concrete floors shall not be acceptable.

Precast ‘beam and hollow pot or block’ type floor construction will not be acceptable.

Once cured, concrete floors to enclosures containing Indoor Equipment shall be prepared and painted with 2No. coats of a proprietary anti-slip floor paint system strictly in accordance with manufacturer’s recommendations.

With the exception of HV only Switching Stations, galvanised steel haulage eyes shall be cast into the floors of traditional construction building enclosures to facilitate the safe installation of plant. Haulage eyes shall be located such that they do not present a trip hazard.

Damp proof membranes shall be incorporated within enclosures housing Indoor Equipment.

12.5.7.1 Floor Design Note:

While dead, imposed and dynamic loadings/actions on floors for approved plant and equipment are available from the manufacturers for detailed structural design purposes, in particular with respect to applied concentrated loads – equivalent imposed uniformly distributed loading (UDL) to floors from plant and equipment typically will not exceed 5kN/m2 applied over the full floor area for the purpose of foundation design.



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12.5.8 Cable Trenches

Cable trenches within enclosures housing Indoor Equipment shall have continuous reinforced concrete bottoms and reinforced concrete or masonry sides.

Cable pits and ramps to substations containing Indoor Equipment shall be sand filled with minimum 50mm granolithic thick screed over flush to floor level on completion, paying particular attention to achieving full compaction of dry sand in layers and sealing of cable entry points in order to ensure that potentially hazardous cavities cannot develop beneath the screed.

Constructors shall fit and remove upon completion temporary timber covers to trenches as necessary to facilitate safe access prior to installation of Equipment.

12.5.8.1 Cable Entries

Cover to cables external to substation buildings shall have minimum statutory ground cover.

Cable pits and ramps to substations containing Indoor Equipment shall be sand filled with minimum 50mm granolithic thick screed over flush to floor level on completion, paying particular attention to achieving full compaction of dry sand in layers and sealing of cable entry points in order to ensure that potentially hazardous cavities cannot develop beneath the screed.

Ducts shall be provided to the express requirements of SPEN where there is concrete surfacing over, or other potential obstruction within cable entry areas that cannot reasonably be avoided.

12.5.9 Masonry / Wall Construction

Masonry units and associated ancillary items shall be as detailed for ‘Masonry’ in this Specification

Solid walls or inner leaves of cavity walls that enclose High Voltage Equipment (switchgear or transformers) or support ‘LV’ boards shall be solid brickwork construction minimum 215mm overall thickness. Walls shall be fair-faced plumb and smooth to the interior.

SPEN accept that double stretcher collar-jointed construction may be necessary where differing masonry units are utilised to inner and outer faces of single leaf solid 215mm thick walls to ‘LV’ board/transformer substations, or where the dimensional tolerance of the required brick units is such that an acceptable even surface finish cannot be achieved with bonded construction either internally (equipment mounting) or externally (appearance). Nominal collar-joints to double stretcher construction shall have solid mortar infill between skins.

External walls to enclosures housing Indoor Equipment shall be cavity construction providing an appropriate internal environment that avoids moisture ingress via condensation, in particular external walls shall provide as a minimum standard thermal insulation values in accordance with Table 4.

Given the potential for disruptive failure, the use of such cavity wall construction shall either incorporate an inner supporting skin of minimum solid 215mm thick brickwork construction or the Constructor shall confirm by structural design calculation to the satisfaction of SPEN that a proposed cavity wall panel construction has adequate lateral strength to withstand the design guide overpressure values given below (e.g. for proposed designs incorporating alternative structural steel frame, wind-post or other masonry reinforcement system).

Double-stretcher collar-jointed and cavity wall construction enclosing High Voltage Equipment shall incorporate Type 1 or Type 2 stainless steel wall ties or other proprietary system specifically designed to ensure adequate transfer of lateral load between masonry skins and flexibility for movement. In all cases, ties shall be evenly distributed at maximum 300mm centres vertically and 375mm horizontally, staggered in alternate courses with additional ties at openings.



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The use of blockwork construction shall not be acceptable unless the Constructor has confirmed by structural design calculation to the satisfaction of SPEN that the proposed wall panel construction has adequate lateral strength to withstand the design guide overpressure values given below (e.g. for proposed designs incorporating alternative structural steel frame, wind-post or other masonry reinforcement system).

Masonry design and construction shall incorporate any movement joints and additional reinforcing measures necessary to accommodate and/or resist post-construction movement in wall panels, internal and external, such that they withstand all loading combinations without cracking, deflection or distortion.

12.5.9.1 Masonry Design Note - Disruptive Failure

Whilst it is not possible to measure or reasonably quantify the magnitude of any potential overpressure, experience over many years has demonstrated how typical substation construction types behave (or fail) in containing and/or relieving the associated overpressure. The guidance given here is based upon that experience, where the greater wall panel design requirements for increasing panel size appear to be offset by the increase in room volume available to dissipate overpressure.

For guidance information only with respect to possible alternative masonry panel design options referenced above, Constructors may wish to note that the lateral design resistance offered by the construction details given in this Specification typically equate to an applied lateral UDL in the order of:

3.5kN/m2 for wall panels of 10/m

2 or less.

1.5kN/m2 for wall panels of 40/m

2 or more.

A linear interpolation value between 3.5kN/m2 and 1.5kN/m

2 for wall panels between

10/m2 and 40m

2.

The minimum 215mm solid brickwork internal wall/inner leaf cavity wall requirements given in this Specification shall be enhanced as necessary for long unrestrained wall panels (e.g. by incorporation of wind posts), such that the lateral design capacity is adequate for this applied design guide overpressure. This is the Constructor’s design responsibility.

While experience indicates that this design guidance may be adequate to prevent collapse, structural damage is likely still to occur.

12.5.10 Roof Construction

12.5.10.1 General

Roofs to enclosures housing Indoor Equipment shall provide as a minimum standard thermal insulation values in accordance with Table 4.

Roofs shall be designed such that they eliminate or protect against the risk of failure due to vandalism or theft; in particular in relation to traditional construction pitched roofs where moisture ingress could lead to disruptive failure if associated with Indoor High Voltage Equipment. For this reason or in relation to the potential for disruptive failure of plant and provision of adequate lateral restraint to the tops of wall panels, traditional construction pitched roofs may require incorporation of a waterproofed structural reinforced concrete slab or other equal approved robust sub-roof construction beneath (not applicable to steel-framed clad building construction).

12.5.10.2 Standard Concrete Roofs

Wherever practicable, roofs should be cast in situ reinforced concrete construction with a fair-faced soffit finish. Slip joints shall be incorporated at wall bearings, polysulphide sealed externally.



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Where alternative preformed solutions are essential these shall be composite construction either:

Proprietary precast pre-stressed beam and in situ concrete screed topping systems with a fair-faced soffit finish, sealed joints and with reinforcement to screed where applicable.

or,

Proprietary metal soffit shutters and in situ reinforced concrete topping systems.

Precast ‘beam and block or pot’ type roof construction shall not be acceptable.

Where permanent structural metal soffit shutters are used as part of a composite roof system these shall be corrosion resistant and the Constructor’s proposals for screening or tagging for earthing purposes shall be expressly agreed with SPEN prior to construction.

12.5.10.3 Flat Roof Design Note

In certain site-specific situations flat roofs to secondary substations may be subject to ‘unusually high’ imposed (‘crowd’) loading from unauthorised personnel access (malicious gatherings or groups seeking a visual vantage point) - it is the Constructor’s responsibility to assess and if necessary design for this risk.

12.5.10.4 Superimposed pitched roofs

Where a pitched roof is required this shall be traditional construction superimposed over the concrete sub-roof and incorporating cross-flow ventilation to the roof space. Alternative proprietary GRP (glass-reinforced plastic) construction pressure relief (lifting) roof systems would be acceptable to substations enclosing Outdoor Equipment (only).

Concrete sub-roofs to substations enclosing Indoor Equipment shall have a nominal waterproof covering applied and a means for rainwater to run-off external to the substation enclosure, to eliminate the risk of moisture ingress related disruptive failure of plant associated with possible failure of the pitched roof.

Facia, bargeboards and the like shall be unplasticised polyvinylchloride construction.

The use of natural slate or lead to pitched roofs should be avoided unless essential for Planning purposes, in order to limit the potential for vandalism and theft.

All timber to pitched roofs shall be vacuum process preservative treated.

12.5.10.5 Integral substation roofs

In the limited instances where there is a compelling reason that a freestanding Secondary Substation enclosing High Voltage Equipment is not practicable and location of a non-standard substation that is attached to or in part integral within other buildings is essential and acceptable in principle to SPEN, integral substation roofs that form the floor to building space over these shall be tanked construction or otherwise incorporate a suitable superimposed waterproof barrier system that is acceptable to SPEN.

12.5.11 Waterproof Coverings to Roofs

12.5.11.1 General

Single membrane systems that are vulnerable to accidental damage from impact and concentrated point loads or from deliberate vandalism (objects thrown onto roofs, malicious use of sharp objects) shall not be acceptable without protective coverings over, in particular where manufacturer’s typically



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describe these products as “suitable for limited foot traffic and light loads” or requiring that “care should be taken to avoid sharp objects or concentrated loads”.

Where SPEN will subsequently adopt the civil fabric of the substation, waterproof covering systems shall include an independent insurance backed guarantee to warranty both materials and workmanship for a period of at least 20 years.

The use of coping stone edge systems shall be avoided as these are particularly susceptible to vandalism.

12.5.11.2 Liquid applied waterproofing paint systems

Liquid applied waterproofing paint systems to exposed concrete roofs shall comprise preparation and two coat high performance (aliphatic) polyurethane systems (flat roofing grade) with purpose designed glass fibre mat reinforcement embedded into the initial coat.

12.5.11.3 Built-up felt waterproofing systems

Built-up felt waterproofing systems to concrete roofs shall comprise preparation, vapour barrier and minimum two-layer polyester reinforced high-tensile high-performance elastomeric felts with mineral surface finish top sheet taken, where applicable, full width over parapet upstands.

Where applicable, roof-edge trims shall be GRP construction.

12.5.11.4 Insulated systems to HV only Switching Station & ‘D’/’G’ Type Substations

Insulated systems to HV only type Switching Stations shall additionally incorporate a venting base layer over insulation board. Insulated systems shall not be installed to substations with designed ventilation for cooling purposes (e.g. cooling to transformers).

12.5.11.5 Mastic asphalt waterproofing systems

Mastic asphalt waterproofing systems to concrete roofs shall comprise preparation and two-coat roofing grade mastic asphalt not less than 20mm thick overall, laid to break joint and incorporating sheathing felt underlay beneath.

Upstands and apron downstands shall not be less than 12mm thick overall, incorporating fillets and galvanised metal backing fixed to the substrate.

Asphalt systems shall receive two coats of solar reflective paint finish.

12.5.11.6 Built-up GRP waterproofing systems

GRP waterproofing systems to concrete roofs shall be proprietary built-up systems, proposed details of which shall be submitted to SPEN for comment and acceptance prior to commencement.

As a minimum, built-up GRP systems shall comprise preparation, exterior quality treated timber decking mechanically fixed to the concrete sub-roof, pre-formed GRP edge trims, lamination with GRP 450gsm fibreglass matting to decking joints, GRP 450gsm fibreglass mat between two layers of polyester resin to form the main waterproof barrier and protective polyester topcoat.

12.5.12 Rainwater Goods

Wherever practicable, designs incorporating rainwater goods should be avoided where the Company will subsequently adopt the civil fabric of the substation.

Where rainwater goods are provided these shall be PVCu construction or other acceptable robust corrosion resistant systems by express agreement with SPEN.



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Gutters and down pipes shall be external to buildings.

Down pipes may require anti-climb and/or anti-vandal guards, subject to the site-specific location.

12.5.13 Woodwork

All timber should be sourced from plantations where accepted management systems are in operation that achieve sustainability of supply.

12.5.14 Doors

It is essential that SPEN personnel can access and properly secure on egress all doors at all times. Any door material/construction type that may bind, shrink, warp, wind, corrode or distort will not be acceptable.

Doors shall be of robust construction that offers a high degree of security against unauthorised entry.

The number of doors having external locking to access buildings shall be kept to a minimum consistent with adequate safe operational use (to limit opportunities for unauthorised entry).

Doors shall open outwards.

Doors shall not open over public highway (i.e. including footways).

Subject to site layout, external doors may be required to open through 1800 to facilitate the installation

of Equipment.

Doors shall be fully weathered including appropriate seals to the external perimeter of frames, cover plate to meeting styles and weather bar to thresholds. Weather bars shall be corrosion resistant construction, built-into concrete thresholds to form weathered faces not exceeding 15mm and flush with finished floor level to avoid presenting a trip hazard.

Doors to substations located in areas of medium, high or very high risk of vandalism or unauthorised entry shall be proprietary security standard doors.

All external access lock mechanisms to substation doors that utilise padlocks shall incorporate integral security shrouds to prevent malicious access to locks.

Proposed door construction details shall be submitted to SPEN for comment and shall be subject to SPEN acceptance in principle prior to procurement, however; irrespective of location and risk, metal security doors are the preferred option type for external substation doors.

12.5.14.1 External metal security doors (preferred type)

External metal security doors shall be proprietary corrosion resistant steel or aluminium units.

Corrosion resistance shall satisfy the specified requirements for design life and time to first maintenance.

Manufacture shall be such that these are sealed against water entry but allow discharge of condensation where it is possible for this occur within.

Metal security doors shall be bonded to the substation earth system in accordance with the requirements of this Specification.



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12.5.14.2 External timber doors

Where external timber doors are necessary for aesthetic reasons (e.g. a planning requirement or to match adjacent existing) these shall be constructed in durable hardwood that is resistant to decay, dimensionally stable and well-seasoned to attain a moisture content within +/- 10% of average equilibrium moisture content.

Experience over many years has demonstrated that double ledge and brace framed tongue and grooved board construction using the best commercial grade West African Iroko (milicia exelsa or milicia regia) hardwood satisfies specified performance requirements. Typical deemed to satisfy external timber door construction guidance drawings are available from SPEN but Constructors shall note that these are generic only and are not indicative of any project-specific requirements such as dimensions, handing, locking etc..

Frames shall be built-in to all new work using galvanised fishtail or ragged right-angled lugs. Frames shall be built-in to existing work using proprietary corrosion resistant frame fixings, pelleted or similarly sealed on completion.

External timber doors shall receive a protective decorative finish that is consistent with specified time to first maintenance, comprising as a minimum two-coat preservative basecoat and two-coat high performance wood stain system or; primer coat, undercoat and two-coat high performance paint system - all with an additional preservative basecoat or primer to all end grain. Protective decorative finishes shall be complete proprietary built-up external wood stain or paint systems that are water repellent and have appropriate designed levels of 'moisture vapour permeability'.

12.5.14.3 External GRP doors

External GRP doors shall be proprietary units of reinforced construction and exposed surfaces that adequately limit surface spread of flame and fire propagation. GRP doors shall be units that offer close tolerances of overall fit and meeting style closure.

Where timber is incorporated this shall be vacuum process preservative treated and fully encapsulated within GRP.

Frames shall be built-in to all new work using galvanised fishtail or ragged right-angle lugs. Frames shall be built-in to existing work using proprietary corrosion resistant frame fixings, mastic sealed to prevent moisture ingress to any encapsulated timber.

12.5.14.4 Internal doors

In the limited instances where there is a compelling reason that a freestanding Secondary Substation enclosing High Voltage Equipment is not practicable and location of a non-standard substation that is in part integral within other buildings is essential and acceptable in principle to SPEN, internal doors shall be proprietary timber or steel fire doors certified as having a fire resistance rating of at least 2-hour and shall facilitate emergency egress.

12.5.14.5 Door furniture

The Constructor is responsible for the supply and installation of all fixed door furniture, which shall be robust heavy-duty construction and corrosion resistant. The Constructor shall agree the type and designated category of user access for locking mechanisms with SPEN on a site-specific basis – SPEN will provide approved locksmith contact details for the supply of SPD, SPT and SPM suited locking mechanisms.

Doors designated as normal points of access shall be minimised (i.e. those having external locking), all other doors shall not have mechanisms for external access.



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Lock bracket or other mechanisms to receive padlocks shall be hardened galvanised or stainless steel high-security lock-brackets, tamper resistant and non-removable without access into the substation.

Lock bracket mechanisms to receive padlocks shall incorporate integral shrouds such that padlocks are protected against unauthorised removal.

Mechanisms for emergency egress shall be high-security multi-point locking mechanisms operated by means of full width panic bars. If emergency escape mechanisms are fitted to access doors with external locking then the panic bars must operate when the doors are locked.

Bolts to fixed leafs shall be solid heavy-duty 16mm square section bow handle galvanised steel or other similar robust corrosion resistant construction.

Doors shall be fitted with appropriate proprietary garage type restraint stays to fix doors open at 900

or, where access for plant installation is restricted, doors shall be fitted with heavy duty galvanised or stainless steel cabin hooks systems to restrain doors open at 180

0.

Hinges shall be stainless steel construction.

Where provided as essential external pull handles shall be appropriately designed heavy-duty galvanised or similar corrosion resistant construction. Pull handles shall be avoided where these have the potential to assist forced unauthorised entry.

12.5.14.6 Door Design Note:

Site-specific requirements for door dimensions, handing and furniture may vary from that indicated in typical guidance drawings listed in this Specification or that indicated in any additional layout or construction detail drawing(s) that may be issued for guidance with respect to external doors. These design matters are the entirely Constructor’s responsibility.

12.5.15 Internal Finishes (Decoration)

Dust can be a significant contributory underlying cause of disruptive failure and minimum internal decoration shall be carried out to reduce this risk as follows:

Preparation & minimum two-coat proprietary anti-slip paint to floors (typically colour grey).

Other decoration shall be carried out as necessary to ensure the adequate ongoing safe operation of the substation and to minimise the requirement for maintenance access, including any necessary ‘top-up’ decoration to make good in the event of damage incurred during installation and commissioning of Equipment.

The use of materials to wall and ceiling finishes that present a dust risk shall be avoided therefore decoration to these should not be necessary.



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13. BUILDING SERVICES TECHNICAL REQUIREMENTS

13.1 Heating & Ventilation

13.1.1 General Requirements

The Building Services shall be designed and constructed such that they provide an environment suitable for the electrical plant to operate and function in accordance with the manufacturer’s requirements.

Where it is proposed to utilise an existing building to house new switchgear then the existing building should be assessed against the requirements detailed below or the specific switchgear requirements, whichever are more onerous.

13.1.2 Heating

Buildings shall be designed to control heating within the following limits for a daily average ambient external temperature range of -10

°C and +30

°C:

Minimum +5°C and maximum +30°C within dehumidified rooms.

Minimum +17°C and maximum +30°C within non-dehumidified traditionally heated rooms

SPEN recognise and accept that it is not economically viable to limit internal temperatures in all circumstances. In extreme weather situations where the external ambient temperature range is outside the range -10°C and +30°C as a short-term and infrequent occurrence the above limits on internal temperatures may be relaxed as follows:

Minimum +5°C and maximum +35°C within dehumidified rooms.

Minimum +5°C and maximum +35°C within non-dehumidified traditionally heated rooms.

Substations that do not contain heat generating plant shall be heated via electrical heaters installed and controlled, to achieve the minimum temperatures stated above, by thermo-switches. The heaters shall be locked off against tampering with a manual override switch, with a 2-hour maximum timer, fitted to allow an increase in ambient temperature to 21°C during occupation.

13.1.3 Insulation

Insulation shall not be provided to heat generating transformer substations, thermal transmittance values to these buildings shall be nominal only to the extent that problems associated with condensation are prevented (i.e. given the transformer is a heat source).

Insulation shall be provided to the walls and roofs of substations that contain Indoor Equipment but have no heat generating plant (e.g. HV only Switching Stations or ‘D’/’G’ Type Substations) such that these have, as a minimum, thermal insulation values to walls and roofs in accordance with Table 4.

Region Roof

U (W/m²K) Walls

U (W/m²K)

Scotland 0.2 0.27

England & Wales 0.25 0.35

Table 4 – Thermal Insulation Requirements



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13.1.4 Ventilation

Ventilation design shall control humidity such that this ensures the safe, efficient operation of the substation and to prevent any undue deterioration of the plant, equipment or fabric of the enclosure, in particular to prevent problems associated with condensation.

Relative humidity shall be maintained between 20% and 75% and the preferred method to control humidity in HV only Switching Stations or ‘D’/’G’ Type Substations that have no heat generating plant is natural ventilation. Ventilation shall be nominal trickle ventilation only to prevent problems associated with condensation; typically airbricks or the like providing natural air flow across the room from low to high-level through outside walls.

Adequate natural ventilation shall be provided to dissipate heat generated by transformers and/or to prevent condensation, which requires location against outer walls in the limited instances where a preferred/optimum freestanding location is not practicable and where therefore substations are integral within third party buildings. Designers should refer to SUB-02-006 for typical heat generation values for 500kVA and 1000kVA transformers.

There should be a minimum 1m clear external to walls incorporating vents. These walls shall be located such that they are adequately clear of areas that may be a fire risk, be dusty or have potentially hazardous gas or chemicals in the air.

Ventilation shall be achieved by natural airflow through outside walls across heat generating plant, and shall not be less than the equivalent areas indicated by the typical guidance drawings given in SUB-02-006 and as listed in this Specification. Experience over many years has demonstrated that this level of natural ventilation is adequate in the majority of situations; however, designers should note that certain supply conditions might require additional or alternative ventilation arrangements.

Ventilation arrangements that short-circuit the airflow would not be acceptable.

Ventilation units shall be of robust vandal and corrosion resistant construction.

Ventilation units shall incorporate appropriate seals to the external perimeter.

Intumescent vent units shall be provided where segregation in the event of fire is required.

Vents to enclosures housing Indoor Equipment shall be secure and weathered to offer a degree of protection not less than that of IP35D to BS EN 60529 and evidence of type testing for ingress protection shall be available. Furthermore, the construction of these ventilation units shall be such that long object probes of any type and cross-section do not have the potential to infringe safety clearance distances from hazardous parts. Galvanised or stainless steel ‘Z’ vent construction details indicated by typical “deemed to satisfy” guidance drawings listed in this Specification satisfy SPEN’s performance requirements with respect to such vents

13.2 Electrical Services

13.2.1 General

Electrical installation schemes shall be compliant with SUB-03-012 and entirely suitable to the intended purpose in the substation building,

The scheme shall conform in all respects to the requirements of the relevant British Standards and the Regulations for the Electrical Equipment of Buildings issued by the Institution of Electrical Engineers (IEE) or its successor organisation. In addition, lighting shall be in accordance with the appropriate CIBSE publication.

The Constructor shall submit his proposals to SPEN for approval prior to commencing work.



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The Constructor shall make available for inspection a valid electrical test certificate for the works in accordance with the current IEE regulations, including where applicable incorporation within CDM H&S File handover to SPEN.

Internal cabling shall be run through surface-mounted conduit.

13.2.2 Small Power

Buildings shall incorporate complete electrical installations for lighting and small power schemes including 400V, 230V and 110V outlet sockets as required by SPEN.

Low voltage systems will be designed to be compatible with the low voltage installation for the requirements of the plant operation.

13.2.3 Internal Lighting

Internal lighting shall allow safe movement of personnel and safe operation of equipment. Lighting shall be operated by wall switches positioned adjacent to doorways. It shall also incorporate a 4 hour timer manual override switch.

Internal lighting schemes generally shall be designed such that the positions of all light fittings and associated switches etc. take due cognisance of the locations of all equipment and access/egress routes within the building.

Emergency lighting shall also be provided in accordance with BS 5266-1. A key test wall switch shall be installed adjacent to the entrance door.

13.2.4 Electro-mechanical heating, ventilation & air conditioning systems

Where provided electrical installations for heating, ventilation and air conditioning schemes to buildings shall incorporate control and instrumentation, interlocking and cabling systems necessary to maintain appropriate operational conditions. The use of air conditioning shall be avoided.



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14. POST-COMMISSIONING (RETURN) SITE VISIT

Programming is outside the scope of this document but Constructors shall note for information that civil works return visits to sites are necessary typically between one and six months after substantial completion (i.e. after handover for equipment installation) to complete post-commissioning finishing civil and building works that may include but may not be exclusively limited to:

Sand fill/screed to cable trenches within buildings.

Sealing cable entries against moisture and vermin entry where this has not otherwise been completed as part of equipment installation and commissioning works.

Making-good original decoration within buildings where this has been damaged during installation of Equipment.

Making-up ground levels as necessary and stone chipping topping or other agreed finishes to compounds.

Where the substation has become operational under SPEN Safety Rules all Constructor operatives subsequently working at the substation shall have appropriate Scottish Power Authorisation(s).



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15. DRAWINGS

Guidance Drawings such as those listed below may be available from SPEN indicating Typical Layout and Construction details that are deemed to satisfy with respect to SPEN’s functional civil and building requirements for Secondary Substations. Constructors shall note that where provided such typical details may be generic and may not reflect exactly actual requirements on a project/site-specific basis.

Typical Traditional Building Details for Single ‘LV’ Board/Transformer Substations

(Indoor Equipment)

Typical Traditional Building Details for Double ‘LV’ Board/Transformer Substations

(Indoor Equipment, rectangular layout)

Typical Traditional Building Details for Double ‘LV’ Board/Transformer Substations

(Indoor Equipment, square layout)

Typical Traditional Building Details for 11kV Unit Substations

(Outdoor Equipment)

Typical Foundation Plinth Details for GRP Container 11kV Unit Substation

(Outdoor Equipment, with/without RMU/Metering)

Typical Traditional Building Details for HV Only Panel Board Switching Stations

Typical Traditional Building Details for Generation related ‘D’ or ‘G’ Type Substations

(Indoor-Outdoor Equipment)

Typical Foundation Plinth Details for GRP Container ‘D’ or ‘G’ Type Substations

(Indoor-Outdoor Equipment)

Typical Hardwood Door Construction Details for Secondary Substations

(i.e. where these are necessary as an alternative to the preferred metal security doors)

Typical ‘Z’ Vent Louvred Ventilation Units for Traditional Secondary Substation

Where applicable and considered appropriate by SPEN, additional typical deemed to satisfy construction detail drawings may be issued on a project-specific basis.